1. Field of the Invention
The present invention generally relates to a display device, and more particularly to a liquid crystal display device with high transmittance, less flicker.
2. Description of Prior Art
Flicker is a visual defect to an AMLCD (Active Matrix Liquid Crystal Display) which has already been led a great concern in the related industry field. Various kinds of solutions have proposed to minimize the flicker phenomenon occurring on a liquid crystal display. For example, voltage adjustment, flicker compensation circuit design, gate R-C loading degradation, Cst (storage capacitance) compensation, and etc. Among those solutions, the Cst compensation can be a major choice for the manufacturers of liquid crystal display in general.
Please refer to FIG. 1, which depicts a top view of a simple conventional structure of a pixel unit O according to prior art. As shown in FIG. 1, a pixel unit O includes a gate line 10, a data line 20, a polysilicon layer 30 as an active channel region of a TFT (Thin Film Transistor) of the pixel unit O, a Cst (storage capacitance) line 40 and a Cst (storage capacitance) 50. The Cst (storage capacitance) 50 is formed between the polysilicon layer 30 and the Cst (storage capacitance) line 40. The pixel unit O further includes a top ITO (Indium Tin Oxide) 102, and a contact hole 112. All aforesaid elements respectively have generally well known functions and occupy certain areas of the pixel unit O.
Please refer to FIG. 2 and FIG. 3. FIG. 2 shows a diagram showing relationship between a flicker level denoted in decibel value and a voltage difference between Vsc and Vcc of a liquid crystal display. Vcc represents a supply voltage to the liquid crystal display. Vsc represents a storage capacitance voltage to the liquid crystal display. As shown in FIG. 2, small, middle and great total storage capacitance/a gate width ratios (Ctotal/W) are shown, when a greater total storage capacitance/a gate width ratio (Ctotal/W) is adopted, the flicker level becomes lower and the flicker is reduced. FIG. 3 shows a relationship diagram of a flicker decibel value and a total storage capacitance/a gate width ratio (Ctotal/W) of a liquid crystal display. Apparently, the flicker level becomes smaller and therefore the flicker can be reduced as the Ctotal/W becomes greater. Ctotal is a sum of Clc (capacitance of the liquid crystal) plus Cst and W is the gate width.
In the foregoing Cst compensation solution for reducing the flicker, a larger Ctotal value is preferred and a large Cst area is required in order to minimize the flicker phenomenon. However, similar to the gate line 10 and the data line 20, the Cst line 40 is generally made by metal material. Unlike the top ITO 102 which is transparent as well known and is employed as the pixel electrode of the pixel unit O, the Cst line 40 is not transparent so the light cannot penetrate therethrough. Accordingly, when the Cst area is enlarged to minimize the flicker phenomenon, the transmittance of the whole liquid crystal display unavoidably becomes low.
In related manufacturing industries today, there is a need to develop a better solution for resolving the aforesaid problem, consequently.